In recent years, technologies for making it possible to vary the compression ratio of an internal combustion engine with a view to improve performance of the internal combustion engine in terms of gas mileage and power etc. have been proposed. In an already proposed technology as such, a cylinder block and a crank case are linked in such a way as to allow their movement relative to each other, and a cam shaft is provided in their link portion to displace the cylinder block and the crankcase toward and away from each other by turning the cam shaft, as disclosed in Japanese Patent Application Laid-Open Nos. 7-26981 and 2003-206771.
In the aforementioned variable compression ratio internal combustion engine, the compression ratio of the internal combustion engine is changed in accordance with the running condition of it so as to prevent knocking in the internal combustion engine and ensure sufficient thermal efficiencies.
On the other hand, as disclosed for example in Japanese Patent Application Laid-Open No. 5-149142, internal combustion engines equipped with an exhaust turbine driven supercharger (or a turbocharger, which will be simply referred to as a “supercharger” hereinafter) that is driven by the exhaust gas provided in an exhaust passage of the internal combustion engine have been conventionally known. The supercharger is a apparatus in which a turbine is turned utilizing energy of the exhaust gas discharged from the cylinder thereby compressing air by means of a compressor attached to the rotary shaft same as the turbine shaft and supplying the compressed air into the cylinder.
In internal combustion engines in which the above-described technologies are used in combination, if response delay of the supercharger is large, when a request for acceleration is made to the internal combustion engine by, for example, pressing the accelerator pedal, the time lag between pressing of the accelerator pedal and rising of the supercharging pressure becomes long, which sometimes makes it difficult to achieve satisfactory acceleration performance. In connection with this, various technologies have been proposed: Japanese Patent Application Laid-Open Nos. 2002-70601 and 2-163429 teach to retard compression ratio reduction control in accordance with delay in the supercharging pressure upon acceleration to prevent a decrease in the torque in the early stage of acceleration; Japanese Patent Application Laid-Open No. 2001-342859 teaches to reduce the compression ratio with an actual increase in the supercharging pressure thereby preventing knocking form occurring; Japanese Utility Model Application Laid-Open No. 63-150048 teaches to set the compression ratio in such a way that the higher the load is the lower the compression ratio is and to set a supercharging pressure as a control target in accordance with the compression ratio thereby preventing knocking from occurring during acceleration; Japanese Patent Application Laid-Open No. 2004-156464 teaches to delay compression ratio reduction control in accordance with delay in rising of the temperature at the exit of an intercooler during acceleration to prevent a decrease in the torque in the early stage of acceleration during which knocking is hardly to occur.